Transmissions of motor vehicles having shift elements, including both positively locking shift elements and frictionally locking shift elements, are known from practice. In each selected gear ratio of such a transmission, a first number of shift elements of the transmission is closed or engaged and a second number of shift elements of the transmission is opened or disengaged, wherein when a gear change from a current gear ratio into a target gear ratio is carried out, at least one previously closed shift element is opened or disengaged and at least one other previously opened shift element is closed or engaged.
If a positively locking shift element has to be closed or engaged in order to carry out a gear ratio change or a shift operation in the transmission, the positively locking shift element must close in a defined rotational speed window about a target differential rotational speed in order to avoid damage to the positively locking shift element. In order to ensure this closing within the defined rotational speed window, it is already known from practice to perform synchronization of the positively locking shift element, specifically by at least partially closing a frictionally locking shift element, in order to carry out a gear ratio change during which a positively locking shift element has to be closed or engaged.
In addition it is necessary to monitor whether a positively locking shift element which is to be opened is actually opened or disengaged in order to avoid over determinacy of the transmission. It is therefore possible when opening a positively locking shift element to bring about a seizure which can lead to a situation in which the positively locking shift element which is to be opened does not open.
It is also already known from practice to operate a motor vehicle with such a transmission in a sailing mode. In a sailing mode of the motor vehicle, the shift elements of the transmission are actuated such that one single shift element of the transmission less is closed, and therefore one single shift element of the transmission more is opened, than in a selected, force locking gear ratio.
In this context, it is also already known, in the sailing mode of the motor vehicle, to adjust or adapt or change the respectively closed and respectively opened shift elements of the transmission as a function of at least one operating condition of the motor vehicle, so that the sailing mode of the motor vehicle can be exited within the shortest possible time. During the adjustment of the respectively closed and respectively opened shift elements in the sailing mode, it may be necessary to open at least one previously closed, positively locking shift element of the transmission. This must be monitored.
DE 10 2013 213 239 A1 discloses a motor vehicle having a transmission which includes a plurality of positively locking shift elements and a plurality of frictionally locking shift elements. The positively locking shift elements are dogs and the frictionally locking shift elements are clutches and brakes. With the transmission known from DE 10 2013 213 239 A1 it is possible to make available in total nine forward gears and one reverse gear ratio. In this context, a converter is connected between a transmission input shaft of the transmission and a drive assembly.